Acquired Nisin Resistance in Staphylococcus aureus Involves Constitutive Activation of an Intrinsic Peptide Antibiotic Detoxification Module

Resistance to the lantibiotic nisin (NIS) arises readily in Staphylococcus aureus as a consequence of mutations in the nsaS gene, which encodes the sensor kinase of the NsaRS two-component regulatory system. Here we present a series of studies to establish how these mutational changes result in reduced NIS susceptibility. Comparative transcriptomic analysis revealed upregulation of the NsaRS regulon in a NIS-resistant mutant of S. aureus versus its otherwise-isogenic progenitor, indicating that NIS resistance mutations prompt gain-of-function in NsaS. Two putative ABC transporters (BraDE and VraDE) encoded within the NsaRS regulon that have been reported to provide a degree of intrinsic protection against NIS were shown to be responsible for acquired NIS resistance; as is the case for intrinsic NIS resistance, NIS detoxification was ultimately mediated by VraDE, with BraDE participating in the signaling cascade underlying VraDE expression. Our study revealed new features of this signal transduction pathway, including that BraDE (but not VraDE) physically interacts with NsaRS. Furthermore, while BraDE has been shown to sense stimuli and signal to NsaS in a process that is contingent upon ATP hydrolysis, we established that this protein complex is also essential for onward transduction of the signal from NsaS through energy-independent means. NIS resistance in S. aureus therefore joins the small number of documented examples in which acquired antimicrobial resistance results from the unmasking of an intrinsic detoxification mechanism through gain-of-function mutation in a regulatory circuit. IMPORTANCE NIS and related bacteriocins are of interest as candidates for the treatment of human infections caused by Gram-positive pathogens such as Staphylococcus aureus. An important liability of NIS in this regard is the ease with which S. aureus acquires resistance. Here we establish that this organism naturally possesses the cellular machinery to detoxify NIS but that the ABC transporter responsible (VraDE) is not ordinarily produced to a degree sufficient to yield substantial resistance. Acquired NIS resistance mutations prompt activation of the regulatory circuit controlling expression of vraDE, thereby unmasking an intrinsic resistance determinant. Our results provide new insights into the complex mechanism by which expression of vraDE is regulated and suggest that a potential route to overcoming the resistance liability of NIS could involve chemical modification of the molecule to prevent its recognition by the VraDE transporter

How Human Herpesviruses Subvert Dendritic Cell Biology and Function

In the last decades, a multitude of distinct herpesvirus-mediated immune evasion mechanisms targeting dendritic cell (DC) biology were uncovered. Within this chapter, we summarize the current knowledge how herpesviruses, especially the α-herpesviruses HSV-1, HSV-2, varicella-zoster virus (VZV), and the β-herpesvirus HCMV, shape and exploit the function of myeloid DCs in order to hamper the induction of potent antiviral immune responses. In particular, the main topics covering herpesvirus-mediated immune evasion will involve: (i) the modulation of immature DC (iDC) phenotype, (ii) modulation of iDC apoptosis, (iii) the inhibition of DC maturation, (iv) degradation of the immune-modulatory molecule CD83 in mature DCs (mDCs), (v) interference with the negative regulator of β2 integrin activity, cytohesin-1 interaction partner (CYTIP), (vi) resulting in modulation of adhesion and migration of mDCs, (vii) autophagic degradation of lamins to support productive HSV-1 replication in iDCs, (viii) the release of uninfectious L-particles with immune-modulatory potential from HSV-1-infected mDCs, and (ix) the implications of DC subversion regarding T lymphocyte activation

Intelligentes Marketing durch adaptive Produktpräsentation im Web

Mit zunehmender Verbreitung entwickelt sich das World Wide Web zu einem von Produkt- und Marketing-Infomationen dominierten Dienst, in dem verstärkt multimediale Gestaltungsmittel von Interesse sind. Da diese Präsentationen wegen des hohen Datenvolumens und der verschiedenen Hard- und Software-umgebungen der Kunden nicht nur auf Begeisterung stoßen, ist es jedoch wünschens-wert, die Darstellung der Produkte individuell an die Interessen und Vorlieben der Kunden zu adaptieren. In diesem Beitrag wird das TELLIM-System vorgestellt, welches den Kunden bei seinen Interaktionen mit den multimedialen Präsentationselementen beobachtet und daraufhin die Produktpräsentationen mit Hilfe eines inkrementeilen Lemverfahrens zur Laufzeit auf den einzelnen Kunden abstimmt

The Polycyclic Polyprenylated Acylphloroglucinol Antibiotic PPAP 23 Targets the Membrane and Iron Metabolism in Staphylococcus aureus

Recently, a series of endo-type B polycyclic polyprenylated acylphloroglucinols (PPAP) derivatives with high antimicrobial activities were chemically synthesized. One of the derivatives, PPAP 23, which showed high antimicrobial activity and low cytotoxicity, was chosen for further investigation of its bactericidal profiles and mode of action. PPAP 23 showed a better efficacy in killing methicillin resistant Staphylococcus aureus (MRSA) and decreasing the metabolic activity of 5-day-old biofilm cells than vancomycin. Moreover, S. aureus did not appear to develop resistance against PPAP 23. The antimicrobial mechanism of PPAP 23 was investigated by RNA-seq combined with phenotypic and biochemical approaches. RNA-seq suggested that PPAP 23 signaled iron overload to the bacterial cells because genes involved in iron transport were downregulated and iron storage gene was upregulated by PPAP 23. PPAP 23 affected the membrane integrity but did not induce pore formation; it inhibited bacterial respiration. PPAP 23 preferentially inhibited Fe–S cluster enzymes; it has a mild iron chelating activity and supplementation of exogenous iron attenuated its antimicrobial activity. PPAP 23 was more effective in inhibiting the growth of S. aureus under iron-restricted condition. The crystal structure of a benzylated analog of PPAP 23 showed a highly defined octahedral coordination of three PPAP ligands around a Fe (3+) core. This suggests that PPAPs are generally capable of iron chelation and are able to form defined stable complexes. PPAP 23 was found to induce reactive oxygen species (ROS) and oxidative stress. Fluorescence microscopic analysis showed that PPAP 23 caused an enlargement of the bacterial cells, perturbed the membrane, and dislocated the nucleoid. Taken together, we postulate that PPAP 23 interacts with the cytoplasmic membrane with its hydrophobic pocket and interferes with the iron metabolism to exert its antimicrobial activity in Staphylococcus aureus

Target protection as a key antibiotic resistance mechanism

Antibiotic resistance is mediated through several distinct mechanisms, most of which are relatively well understood and the clinical importance of which has long been recognized. Until very recently, neither of these statements was readily applicable to the class of resistance mechanism known as target protection, a phenomenon whereby a resistance protein physically associates with an antibiotic target to rescue it from antibiotic-mediated inhibition. In this Review, we summarize recent progress in understanding the nature and importance of target protection. In particular, we describe the molecular basis of the known target protection systems, emphasizing that target protection does not involve a single, uniform mechanism but is instead brought about in several mechanistically distinct ways